As textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. As such, to visually enhance these textile substrates and counteract the fading and yellowing the use of polymeric colorants for coloring consumer products has become well known in the prior art. For example, it is well known to use whitening agents, either optical brighteners or bluing agents, in textile applications. However, traditional whitening agents tend to lose efficacy upon storage due to deleterious interactions with other formulation components (such as, for example, perfumes). Further, such whitening agents can suffer from poor deposition on textile substrates. As such, formulators tend to increase the level of whitening agent used to counteract any efficacy lost upon storage and/or to increase the amount of whitening agent available to deposit on the textile substrate.
Leuco dyes are also known in the prior art to exhibit a change from a colorless or slightly colored state to a colored state upon exposure to specific chemical or physical triggers. The change in coloration that occurs is typically visually perceptible to the human eye. Many of these compounds have some absorbance in the visible light region (400-750 nm), and thus more or less have some color. In this invention, a dye is considered as a “leuco dye” if it did not render a significant color at its application concentration and conditions, but renders a significant color in its triggered form. The color change upon triggering stems from the change of the molar attenuation coefficient (also known as molar extinction coefficient, molar absorption coefficient, and/or molar absorptivity in some literatures) of the leuco dye molecule in the 400-750 nm range, preferably in the 500-650 nm range, and most preferably in the 530-620 nm range. The increase of the molar attenuation coefficient of a leuco dye before and after the triggering should be greater than 50%, more preferably greater than 200%, and most preferably greater than 500%.
Leuco compounds can be used as whitening agents in laundry care compositions (e.g., laundry detergents). In such uses, the addition of the leuco compound, which is an uncolored or only lightly colored state, does not significantly affect the aesthetics of the laundry care composition. Then, the leuco compound can be converted to a colored state in which it imparts the desired whitening benefit to the textile substrate.
The purpose of leuco colorants is generally to visually whiten these textile substrates and counteract the fading and yellowing of the substrates. Typically, leuco colorants may be found in laundry detergents and are therefore applied to textile substrates during the laundering process. When the leuco colorant is in a laundry detergent, however, the consumer does not have the flexibility to customize their desired experience. Extra whitening can be achieved only by adding additional detergent, which necessitates increased and potentially wasteful levels of cleaning ingredients and may also result in deposition of too much fragrance. Thus, the consumer cannot balance their desire for efficient usage of cleaning ingredients, adjusting for the right amount of scent, and yet also be able to deliver variable amounts of whitening according to the needs of the particular fabrics being treated.
As a result, there exists a need for a laundry care composition so that leuco colorant may be used independently as an additive to satisfy the consumer desire for adjustable dose, on-demand whitening while delivering the benefits of a leuco colorant from a particle of low color or color other than that of the leuco colorant.
One of the challenges of delivering whiteness benefits using a hueing technology is that consumers often possess garments that are designed to be lightly colored, such as pastels, and the application of hueing, shading or bluing agents can compromise the intended color for such garments, leading to consumer dissatisfaction. There is a continuing need to develop approaches for hueing that selectively deposit on aged cotton garments (those which are most likely to have developed yellowing over time that can benefit from color correction) and deposit less well on new, clean cotton garments that have no need for color correction.
We have discovered that leuco colorants can display a bias for depositing on consumer-sourced, aged cotton garments over new, clean cotton. Leuco colorants are thus better able to deliver a whitening benefit where it is needed, and avoid hueing new, clean cotton garments where such hueing might well be considered undesirable.
It has surprisingly been found that the laundry care compositions of the present disclosure which incorporate leuco colorants are not only effective at whitening of textile substrates without dictating the color of the composition, but also provide a clean and convenient means to add the consumer-desired amount of a whitening agent to a laundry treatment without adversely impacting the colors of newer garments.